Investigators are optimistic that they can soon locate wreckage from the missing Malaysian Air jet in the Indian Ocean after reacquiring acoustic pings that may emanate from the flight recorders.

Australian search vessel Ocean Shield detected a signal two more times, a possible step toward narrowing the hunt enough to deploy a robot submarine to scan the seabed. The sounds are consistent with those from beacons on black boxes, said retired Air Chief Marshal Angus Houston, who heads Australia’s Joint Agency Coordination Centre.

“Hopefully with lots of transmissions, we will have a tight, small area — and hopefully in a matter of days we will be able to find something on the bottom,” Houston told reporters yesterday in Perth.

The pulses heard on April 8 following two April 5 contacts bolstered authorities’ confidence that they are finally zeroing in on debris a month after Flight 370 vanished. Knowing where to start underwater surveillance is pivotal before committing the Ocean Shield’s sonar-equipped submersible.

The two most recent sounds were faint and partially obscured by background noise, according to Phoenix International Holdings Inc., the Largo, Maryland-based contractor operating the U.S. Navy’s towed pinger locator aboard the Ocean Shield.

‘Very Distinct’

“While they didn’t hold that signal for a long time, it still had a very distinct repetition rate and audible signal,” General Manager Jim Gibson said in an interview. Australia’s JACC said one of the contacts lasted for 5 minutes and 32 seconds, and the other for 7 minutes.

Fading power reserves for the beacons on the Boeing Co. 777-200ER’s cockpit-voice and flight-data recorders add urgency to the search. The batteries are nearing the end of their life span after the Malaysian Airline System Bhd. plane disappeared en route to Beijing from Kuala Lumpur on March 8. On board were 239 passengers and crew members.

Malaysia is “cautiously more optimistic,” Acting Transport Minister Hishammuddin Hussein said in a Twitter posting after Houston’s press conference. “Pray latest leads will help us all move ahead.”

The search area for today was narrowed to 57,923 square kilometers, the JACC said in a statement. Up to 10 military aircraft, four civil aircraft and 13 ships will assist in the operations, about 2,280 kilometers northwest of Perth.

‘Probability Circle’

Aircraft and ships reported spotting a large number of objects during yesterday’s search, according to the statement. Only a small number were able to be recovered, it said.

The Ocean Shield carries an unmanned sub, the Bluefin-21, that is ready to launch and start scouring the seafloor with sound waves once the search zone is refined, Houston said. Water depths in the area exceed about 4,500 meters (14,800 feet), far from any natural light from the surface.

By passing back and forth across the area, the search vessel and the towed pinger locator are “narrowing the probability circle of where the debris field is suspected to be,” said John Fish, a principal of Bourne, Massachusetts-based American Underwater Search & Survey Ltd.

Sounds from the pingers don’t travel as far when the signal weakens, so picking up the new contacts suggests that the Ocean Shield is getting closer to the wreckage, said Fish, whose company has helped recover numerous aircraft and their black-box recorders from underwater.

‘Very Difficult’

The pingers have a range of about 2 miles (3.2 kilometers), according to the manufacturer, Dukane Seacom, a unit of Hollywood, Florida-based Heico Corp. The black-box maker is Morris Township, New Jersey-based Honeywell International Inc.

Dukane Seacom has analyzed data collected on the pings and concluded that the signals “would be very difficult to be anything else than the acoustic signature of a beacon,” President Anish Patel said in a telephone interview. “Does it have to be the black-box beacon? It could be something else, but the likelihood of it being something else is doubtful.”

Analysis of earlier pings heard by the Ocean Shield determined that a “very stable” signal was detected at 33.331 kilohertz and it consistently pulsed at 1.106-second intervals, JACC’s Houston said. Two signals — one lasting two hours and 20 minutes and the other for 13 minutes — were detected after the deployment of the pinger locator. On the second pass, two pinger signatures were recorded simultaneously, Houston said April 7.

Frequency Shift

Dukane Seacom’s pingers are supposed to pulse at 37.5 kilohertz. While the units are designed to have a tolerance of plus or minus one kilohertz from the intended frequency, the difference between the intended signal and the pulses picked up at sea in recent days may not be significant, Patel said.

Tests on a beacon recovered from Air France Flight 447, the jet that crashed in the South Atlantic in 2009, found that the unit had shifted frequency after months on the ocean floor, transmitting at 34 kilohertz, Patel said.

According to a map from the Australian Maritime Safety Authority, the four pings heard so far came from a triangular zone with one side almost 30 kilometers long. The distances between the four detections may be explained by the fact that there are two black boxes, each with a pinger, Fish said.

Even after sending the Bluefin-21 into the water to prowl the ocean bottom with sonar, the search may face complications because of a blanket of silt several meters deep on the seabed, Houston said.

Flight’s End

“I am now optimistic that we will find the aircraft, or what is left of the aircraft in the not-too-distant future,” Houston said. “But we haven’t found it yet because this is a very challenging business.”

Houston said the location of the pings is lining up with other evidence of where the plane may be. The underwater sounds were detected near where analysts estimate a final, partial satellite signal was received from the Malaysian plane, Houston said.

That last pulse to an Inmarsat Plc satellite is where investigators believe the 777’s two engines may have flamed out, Houston said. “It’s probably significant in terms of the end of powered flight,” he said.

The jet’s disappearance is now the longest in modern airline history, baffling authorities because contact was lost less than an hour into a routine trip as Flight 370 headed north over the Gulf of Thailand. After vanishing from radar, the wide- body craft doubled back, flew over Peninsular Malaysia and on into some of the world’s most remote waters.

While the motive behind that heading remains unknown, Flight 370 was deliberately steered south on a path ending in the Indian Ocean, Malaysian Prime Minister Najib Razak has said.

Detecting the pings has transformed the nature of the hunt for clues, Phoenix’s Gibson said.

“At the end of the day it’s not a small area, but it’s an area that is certainly more manageable than starting out with hundreds of thousands of square miles,” Gibson said.

With assistance from John Walcott in Washington, Shamim Adam and Kyunghee Park in Singapore, Jason Scott in Perth, Laura Hurst in London, Zachary Tracer in New York, Michael Heath, Edward Johnson and David Fickling in Sydney and Andrea Rothman in Toulouse. To contact the reporters on this story: Michael Sin in Sydney at [email protected]; Alan Levin in Washington at [email protected]; Thomas Black in Dallas at [email protected] To contact the editors responsible for this story: Bernard Kohn at [email protected]; Ed Dufner at [email protected]; Anand Krishnamoorthy at [email protected]

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